LEWISTON — Just as trees tell their history with rings — marking a year of life with each ring — glaciers, lakes, coral and the ground itself tell their history, geologist Mike Retelle said Friday.

One needs only know where to look, said the Bates College professor and Geology Department chairman.

In his case, an investigation into how much people are responsible for global climate change has taken him to the top of the world, to a remote Norwegian island in the Barents Sea.

Retelle declined to make sweeping conclusions about his work Friday in a lecture with the Great Falls Forum. Rather, he talked about where his study has taken him and some of the patterns that he and other scientists see in the high Arctic.

Over the past 2,000 years, scientists are seeing cyclical changes in the weather, he said. He described a warming period during the medieval period and a cool down from about 1400 to 1850, called “the little ice age.”

“The cool thing about the little ice age is that there were a lot of people on the planet and a lot of historical evidence,” he said. The historical evidence ranges from observations and paintings to postcards to wood carvings that noted where glaciers were and how they receded in the years that followed.

His work in the Arctic has been detailing shrinking glaciers. Since 2004, Retelle started going to the Norwegian island and its village, Longyearbyen. In 2012, he spent months there, from February to June and July to September, sponsored in large part by Bates College.

He and students measured the glaciers’ depth, followed them as they receded and analyzed the sediment they left behind.

“They’re retreating very rapidly,” he said. “The snow line goes up the valley and we’re losing mass.”

Retelle offered no explanation for the retreat. The shrinking of the Arctic glaciers may be felt worldwide, though.

“The more we melt the ice, sea level is going to rise,” he said.

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